A LARGE-SCALE GRID-BASED HYDROLOGICAL MODEL OF THE SEVERN AND THAMES CATCHMENTS

This paper addresses the issues of scale and appropriate model complex ity for large-scale hydrological models. A grid-based hydrological mod el, which employs the UK Meteorological Office: Rainfall and Evaporati on Calculation System, is applied to the Severn and Thames reproduce t he observed mean annual runoff over a 10-year period to within 6% with no prior calibration. The variation in the model performance is stron gly correlated with the linearity of the annual rainfall/runoff relati onship and a climate index. At the monthly scale, runoff routing becom es significant, and the introduction of a two-parameter routeing algor ithm significantly improves the monthly runoff simulations giving effi ciencies of 90% and 88% for the Severn and. Thames respectively The re sults provide guidance to climate modellers looking for efficient and robust land-surface parameterizations, and indicate the potential appl ication. of such a modelling scheme to water resource managers.